Page 149 - YORAM RUDY BOOK FINAL

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5.6 Heart Failure (HF)

Activation Patterns in Heart Failure 304

In more than 30% of moderate-to-severe HF cases, LV activation is delayed 305 . Many of
these patients present with wide QRS on the ECG and a left bundle branch block (LBBB) pattern.
ECGI can provide panoramic maps of ventricular activation. We conducted ECGI in eight HF
patients (six males and two females; New York Heart Association class III-IV) with LV conduction

delay, receiving cardiac resynchronization therapy (CRT) with an implanted biventricular (BiV)
pacing device 304 . Figure 5.13 shows native rhythm (unpaced) activation maps from four patients
(four top rows); activation of a normal heart is shown for comparison in the bottom row. A striking

observation is that RV activation is completely normal in all patients, and the entire activation
delay is localized to the LV. Activation of the RV epicardium starts from an RV breakthrough (RVB)
in the typical normal location (round isochrones), indicating a normally functioning RV
conduction system. There are no regions of slow conduction (no crowding of isochrones) or
conduction block in the RV. The mean duration of RV activation is normal at 25 ms.

In marked contrast to the normal activation of the RV, LV activation is delayed and
abnormal in all patients. The LV activation pattern is spatially heterogeneous with regions of block

(thick black lines) and slow conduction (crowded isochrones). The activation patterns differ greatly
among patients. The region of most delayed activation (blue), considered an optimal site of LV
electrode placement for cardiac resynchronization therapy (CRT), is patient specific. In patient #7
it is basal superior ((A), 134ms, indicated by frame). In patient #1 ((C), 153 ms) it is in the lateral wall,
surrounded by a line of block and slow conduction. In patient #3 ((D), 173 ms) it is basal inferior.

A common occurrence is an anterior line of block that forces the wave front to propagate in a
U-shaped pattern to reach the lateral LV by way of the inferior or apical region 306 .

Cardiac Resynchronization Therapy (CRT) 304,307

The goal of CRT is to restore electrical synchrony through pacing of the RV and LV,
accelerating activation of the most delayed LV region. About 70% of cases show improved
symptoms and LV performance, and improved long-term survival with CRT. However, about 30%

of patients do not respond to CRT 307 . Achieving synchrony with BiV pacing depends on the LV
electrode placement relative to the LV electrical substrate. As shown in Figure 5.13, the region of
most delayed activation is patient specific. Therefore, optimal lead placement requires knowledge

of the activation sequence so that the electrode is optimally placed in the most delayed region.
Moreover, other substrate properties must be considered in the LV lead placement procedure.
For example, in patient #1 a line of block and region of slow conduction surround the most
delayed region. It is doubtful that pacing from this site will capture the LV. These examples
illustrate the importance of knowing the electrical substrate prior to biventricular pacing

electrodes (BiV) implantation for CRT.